The invention relates to a method for the production of natural and/or synthetic carbonates and more particularly calcium carbonates, with an extremely high BET/N.sub.2 specific surface area utilizing an inherently known mill and more particularly an agitating ball mill by wet grinding. Furthermore, the invention relates to an advantageous use of the products of the method.
The wet grinding of carbonates has long been known. Wet grinding is a grinding operation using a liquid vehicle, that is to say a grinding operation in a liquid suspension. Wet grinding generally requires a smaller amount of energy for a given amount of material to be ground, since the viscosity of the liquid, which is greater than that of air, as a vehicle creates more favorable conditions for the transmission of force to the particles to be ground. Simultaneously wet grinding offers the advantage of dust-free grinding.
Mills so far required therefor and more particularly agitating ball mills are also familiar in the art. They generally consist of an either vertically or horizontally arranged, cylindrical grinding container with an axially extending high speed agitating shaft which bears a plurality of agitating arms or agitating disks. The grinding container is charged with grains of sand, steel balls or steatite balls or with similar grinding bodies with dimensions between some tenths of a millimeter to some millimeters. The suspension of material to be ground flows through the grinding space continuously from the bottom to the top or, respectively, from the front to the back and is comminuted by the compressive and the shear-forces between the grinding bodies thrown up by the agitator. The high speed agitator is arranged at the axis. In the upper part or, respectively, in the rear part a screen or a restriction in the form of a gap prevents the escape of grinding bodies. The fineness of grinding is dependent on the type of grinding body and the degree of charging, the ratio between the diameters of the grinding bodies and particle size of the material to be ground, the type of material to be ground, the type of agitating elements and the mean residence time of the suspension in the grinding space.
U.S. Pat. No. 2,323,550, especially the drawing, discloses a method in which oversize product leaving a ball mill is returned into the mill with the purpose of achieving products with a desired specific surface area of, for instance, 20,000 square feet per pound (see the specification, page 4, lines 41 and 42 of that patent). In this respect, however, only that part of the suspension is returned which has not attained the desired particle size. It is consequently not a question grinding with a circulation. The solids content of the suspension is in this method between 30 and 35% (see page 6, right column, lines 51 and 52 of that patent).
European patent publication 83112004.3 (publication number 0 115 586) also discloses a method for the wet grinding of natural and/or synthetic carbonates. In column 1, lines 8 ff of this publication there is a recommendation, which is in line with the general way of thinking in the art, to maintain the maximum possible solids content in the aqueous carbonate suspension to ensure a good grinding effect.
Patent publications GB-1,123,219 and GB-1,309,074 disclose the grinding of a wet calcium carbonate suspension which has a solids content of at least 25% by weight.